Various medical devices have been developed.
Specific examples of such devices include drug eluting coronary stents, which are commercially available from Boston Scientific Corp. (TAXUS®), Johnson & Johnson (CYPHER®), and others. These existing products are based on metallic balloon expandable stents with biostable polymer coatings, which release antiproliferative drugs at a controlled rate and total dose.
Specific examples of polymers for drug eluting polymer coatings include block copolymers, such as block copolymers containing polyisobutylene and polystyrene blocks, for instance, polystyrene-polyisobutylene-polystyrene triblock copolymers (SIBS copolymers), which are described in U.S. Pat. No. 6,545,097 to Pinchuk et al. These polymers have proven valuable in implantable and insertable medical devices for a variety of reasons, including their excellent elasticity, strength and biocompatibility. Moreover, they have proven to be effective drug delivery systems for providing therapeutic agents to sites in vivo.
These and other polymers, however, are typically applied to underlying substrates via spray coating processes, which have a number of less than desirable characteristics including the following, among others: (a) spraying processes typically require a line-of-sight trajectory between the spray source and the surface to be coated, meaning that complete coverage may not be achieved for a variety of substrates, (b) material losses are commonly high for spraying processes, with significant portions of the spray stream not being deposited on the substrate, particularly for substrates which have a significant amount of void space, such as cardiovascular stents, and (c) where a drug is included in the spray coating, it is very difficult to achieve a homogeneous dose distributions over underlying substrate.